deleterious

adj

1. (formal)Harmful, often in a subtle or unexpected way.

   “deleterious effects”

   “deleterious to someone's health”

   “Or might it suffice him, that every wholesome growth should be converted into something deleterious and malignant at his touch?”

   “A trolleybus service was established by the London Passenger Transport Board between North Woolwich and Stratford on February 6, 1938, and had a deleterious effect on railway passenger traffic.”

   “The advent of the smartphone and its cousin the tablet was followed quickly by hand-wringing about the deleterious effects of “screen time.” But the impact of these devices has not been fully appreciated, and goes far beyond the usual concerns about curtailed attention spans.”

2. Having lower fitness.

   “A deleterious mutation”